Process for carrying out endothermic gas reactions

ABSTRACT

Production of hydrogen cyanide is carried out by means of a flame reaction by reacting the feed components in flames produced by a combustible gas mixture and admixing a secondary gas stream into said flames. The secondary gas can flow either parallel to or transversely to the combustible gas. One embodiment of the invention consists in passing ammonia into a hydrocarbon/oxygenflame front. Another embodiment of the invention consists in passing hydrogen or carbon monoxide into the flame front of a hydrocarbon/ammonia/oxygen-flame.

United States Patent Fetting et al. 51 May 9, 1972 54] PROCESS FOR CARRYING OUT 3,342,241 9/1967 Whitesides.... ....431/353 x ENDOTHERMIC G AS REACTIONS 3,504,994 4/1970 Desty et al. ..263/l9 X 3,221,499 12/1965 Hasbrouck.... ....239/424 X [72] Inventors: Fritz Felting, Darmstadt-Eberstadt; 3,267,927 8/1966 Hirschberg ..239/431 X Henning Bockhorn, Darmstadt; Hans- Herbenl, Newlsenburgl 0f Primary Examiner-Edward G. Favors many Attorney-Cushman, Darby & Cushman [73] Assignee: Deutsche Gold-und Silber-Schneideanstalt vormals Roessler, Frankfurt (Main), Ger- [57] ABSTRACT many Production of hydrogen cyanide is carried out by means of a [22] Filed. 27 1970 flame reaction by reacting the feed components in flames produced by a combustible gas mixture and admixing a secon- [21] PP 32,008 dary gas stream into said flames. The secondary gas can flow either parallel to or transversely to the combustible gas. One 52 11.5. C1. ..431 4 263/19 A embdimem invemm" mists Passing ammnia [51] a hydrocarbon/oxygen-flame front. Another embodiment of 53 Field of Search ..431 174, 8, 4; 263/19; the invemb" Passing hydmge" 239/423, 424, 431 ide into the flame front of a hydrocarbon/ammonia/oxygenflame.

[56] Reerences cued 8 Claims, 4 Drawing Figures UNITED STATES PATENTS 3,115,009 12/1963 Ledwith et al. ..239/424 X (M l/ v l l i i PROCESS FOR CARRYING OUT ENDOTHERMIC GAS REACTIONS The invention relates to a process for carrying out endothermic conversion of light hydrocarbon and ammonia into hydrogen cyanide in flames without the use of catalysts.

In the case of this endothermic gas reaction, the required reaction enthalpy must be put at ones disposal on the basis of thermodynamic rules, that is to say at relatively high reaction temperatures. These conditions can be realized among others in flames in which large amounts of energy can be liberated in a small space at a high temperature.

In the case of carrying out said endothermic gas reaction in flames, an exothermic combustion reaction is coupled with an endothermic synthesis reaction. Both partial reactions take place simultaneously one beside the other in the case of onestep processes in the manner of incomplete combustion, while in the case of two-step processes the initial products of the endothermic synthesis reaction are mixed and made to react with the hot combustion gases of one or several energy producing flames. The formed hydrogen cyanide is not stable at the required synthesis temperatures and it has to be converted to a thermodynamically metastable state through considerable cooling after very short reaction times. The required chilling of the hot reaction gases takes place through direct injection of a cooling medium through heat exchangers (DBP 1,159,409) or through dynamic cooling (British Pat. No. 852,072).

According to the invention, higher yields can be achieved by bringing the light hydrocarbon or a part of it to react together with oxygen in flames burning in a stationary manner, and by admixing a stream of gas (secondary gas) into the flame fronts. In a preferred form of'the invention, the endothermic gas reaction is carried out in jet flames which burn in an environment of ammonia as secondary gas. Through jet mixing this ammonia is sucked up from the downstream side by the jet flames and mixed into the flame fronts. In this way the concentration and temperature profiles in the reaction zones can be influenced in such a manner that the synthesis of hydrogen cyanide will take place at higher yields.

In one form of the invention the ammonia is conducted in parallel flow with the combustible gas mixture into a combustion chamber. The combustible gas flows from a nozzle into the combustion chamber and reacts therein in one or more jet flames having a flame front. The ammonia is admixed with the flame front from any suitable means defining a gap around the nozzle from which the combustible gas flows. The mixing process is controlled by suitable selection of the momentum ratio of the two gas streams.

In another form of the invention the secondary ammonia stream is introduced into the combustion chamber from the bottom and the combustible gas mixture is introduced into the chamber from one or more nozzles arranged in the wall thereof slantingly or transversely with respect to the secondary gas stream. The secondary gas stream is admixed with the burning combustible gas mixture and the mixing process is controlled by suitable selection of the momentum ratio of the two gas streams.

In another embodiment of the invention, the reaction is carried out in premixed flames consisting of light hydrocarbon, oxygen and ammonia which burn in an environment of hydrogen or carbon monoxide. The intermingling of the hydrogen or carbon monoxide with the flame can take place in the two ways mentioned above where ammonia is intermingled with hydrocarbon/oxygen jet flames.

The invention will be understood best in connection with the drawings which give illustrative examples of apparatuses for carrying out endothermic gas reactions according to the process of the invention.

F IG. 1 represents a first embodiment of an arrangement according to the process of the invention in longitudinal section;

FIG. 2 is a cross section of the apparatus of FIG. 1;

FIG. 3 shows a second embodiment of an apparatus according to the process of the invention in longitudinal section; and

FIG. 4 is a cross section of the apparatus of FIG. 3.

Referring more specifically to the embodiment of the invention according to FIGS. 1 and 2, a gas mixture 2 of light hydrocarbon and oxygen or of light hydrocarbon and oxygen and ammonia is conducted through a number of nozzles I (here shown as round). Each of the nozzles l is surrounded by a flow channel 3 shown as an annular gap, through which the secondary gas ammonia or light hydrogen or carbon monoxide 4 is conducted. The combustible mixture 2 reacts from the inside nozzles 1 in the form of jet flames 5. Through suitable selection of the momentum ratio of the jet emerging from an opening 1, to the gasemerging from an opening 3, the mixing process can be controlled. The above-mentioned arrangement is surrounded by the walls of the combustion chamber 6, in which the hot reaction gases are cooled off at a suitable place through cooling apparatus 7.

In the embodiment of the invention according to FIGS. 3 and 4, a mixture of light hydrocarbon and oxygen or of light hydrocarbon and oxygen and ammonia is conducted through the nozzles 11, in this case drawn round, and which are located in the wall 16 of the combustion chamber. The secondary gas ammonia, or hydrogen or carbon monoxide 14, flows upwardly in a flow channel 13 (here shown cylindrically). The combustible mixture 12 is reacted beginning at the nozzles 11 in transversely flowing jet flames 15, whereby the secondary gas 14 is sucked in. Through a suitable choice of the momentum ratio of the jet emerging from an opening 11 to the stream 14 of secondary gas, the mixing process can be controlled. At a suitable place, the hot reaction gases are cooled off through a suitable cooling device 17.

In the previously described apparatuses the synthesis of hydrogen cyanide from light hydrocarbons, ammonia and oxygen was carried out with satisfactory yields. This is further illustrated by the following typical examples.

EXAMPLE 1 In the apparatus of FIGS. 1 and 2, a mixture 2 consisting of about 1.5 Nm lh [Nm standard cubic meter] of propane and about 2.7 Nm /h of oxygen (C/O ratio 0.83) was conducted through 19 nozzles l of 1 mm inside diameter into the reaction chamber. Approximately 0.97 Nm /h of ammonia was conducted as secondary gas 4 through the flow channels 3 developed as annular gaps with an outside diameter of 3.5 mm

cyanide (selectively of the reaction). The entire conversion of ammonia amounted to about 89 percent.

EXAMPLE 2 In the apparatus of FIGS. 3 and 4, experiments for the synthesis of hydrogen cyanide were carried out in the combustion chamber. For this purpose, combustible mixtures 12 of various hydrocarbons (see column 2 with volume throughput of the hydrocarbons), ammonia and oxygen were used in the experiments a to g of table 1, with the mixture compositions in column 5 and column 6. The secondary gases 14 used and their volume through-put have been noted in column 3, and the ratio of the streams of volume of combustible mixture 12 to secondary gas 14 in column 4. The yields and selectivities of hydrogen cyanide, related to ammonia, as well as the conversions of ammonia are found in columns 7, 8 and 9.

Corresponding to what has been said previously, in the case of experiments h and i of table I, combustible mixture 12 of propane and oxygen was injected, which burned as transversely flowing jet flames 15 in a secondary gas stream 14 of ammonia. Forexperiment i, the composition of the reaction gases leaving the combustion chamber has been given in column I of table 2; the composition of the gases after a washing with cold, dilute sulfuric acid is found in column 2 and the comstream whereby it is reacting in at least one transversely or position of the residual gases after the HCN absorption, in slantingly flowing jet'flame. column 3. In the case of all experiments mentioned by way of 4. A process according to claim 1 comprising conducting example, the synthesis temperature amounted to about l,400 the secondary gas in parallel flow with the combustible gas C., whereby the flame reactor was operated with a fresh gas mixture 2, said mixture flowing from at least one nozzle means load of about [Nm /h, m 1 into a combustion chamber and reacting therein in at least 7 TABLE 1 Ratio of Yield, Selec- Conver- Secondary the stream pertivity, sion, Experiment Hydrocarbon NmJ/h. gas Nmfl/h. of volume C/N C/O cent percent percent 3.0 1.8 5.1 0.78 78 93 84 3.0 2. 2 2. 9 0.71 66 s2 80 2. 5 2. 1 5. 1 0. 7s 73 s5 85 2.6 2.1 5.1 0.17 58 68 85 3.0 2.5. 5.5 0.52 70 91 3.8 1. 5 5.1 0. 53 70 89 70 4.6 1.1 5.2 0.80 82 94 87 0. 96 4. 5 4. u 0. 85 77 as 87 1. 2 2. 9 3.0 0.81 66 78 85 TABLE 2 one jet flame having a flame front, admixing with said flame front the secondary gas flowing parallel into said reaction chamber from means defining a gap 3 around said nozzle 2 3 means and controlling the mixing process by suitable selection Vol.% Vol.% v of the momentum ratio of the two gas streams.

5. A process according to claim 1 comprising introducing HCN 83 101 the secondary gas stream 14 into a combustion chamber from NHa L8 the bottom of said chamber, introducing the combustible gas 2 1.2 1.5 1.7 mixture 12 into said chamber from at least one nozzle means $8 2-? g? & 11 arranged in the wall thereof transversely or slantingly with L6 respect to said secondary gas stream, admixing said secondary (j l- 1,2 1,5 1,7 gas stream with the burning combustible gas mixture and con- 2 5311 trolling the mixing process by suitable selection of the momen- 1 g 1 turn ratio of the two gas streams.

6. A process according to claim 1 wherein the feed components light hydrocarbon, oxygen and ammonia are reacted What is claimed is: in jet flames produced by a combustible gas mixture and the 1. A process for carrying out the endothermic reaction of ammonia is admixed as the secondary gas stream into said producing hydrogen cyanide from light hydrocarbon, oxygen flames.

and ammonia comprising reacting the feed component's light 40 7. A process according to claim 1 wherein the feed comhydrocarbon, oxygen and ammonia in flames produced by a ponents light hydrocarbon, oxygen and ammonia are reacted combustible gas mixture while admixing a secondary gas in jet flames produced by a combustible gas mixture and stream into said flames. hydrogen or carbon monoxide is admixed as the secondary gas 2. A process according to claim 1 wherein the secondary gas stream into said flames.

is conducted in parallel flow with the'combustible gas mixture 8. A process according to claim 1 wherein the light and the gas mixture is reacting in at least one jet flame. hydrocarbon is selected from the group consisting of methane,

3. A process according to claim 1, wherein the combustible ethane, propane and ethylene.

gas mixture is injected transversely into the secondary gas a: a m a a 

2. A process according to claim 1 wherein the secondary gas is conducted in parallel flow with the combustible gas mixture and the gas mixture is reacting in at least one jet flame.
 3. A process according to claim 1, wherein the combustible gas mixture is injected transversely into the secondary gas stream whereby it is reacting in at least one transversely or slantingly flowing jet flame.
 4. A process according to claim 1 comprising conducting the secondary gas in parallel flow with the combustible gas mixture 2, said mixture flowing from at least one nozzle means 1 into a combustion chamber and reacting therein in at least one jet flame having a flame front, admixing with said flame front the secondary gas flowing parallel into said reaction chamber from means defining a gap 3 around said nozzle means and controlling the miXing process by suitable selection of the momentum ratio of the two gas streams.
 5. A process according to claim 1 comprising introducing the secondary gas stream 14 into a combustion chamber from the bottom of said chamber, introducing the combustible gas mixture 12 into said chamber from at least one nozzle means 11 arranged in the wall thereof transversely or slantingly with respect to said secondary gas stream, admixing said secondary gas stream with the burning combustible gas mixture and controlling the mixing process by suitable selection of the momentum ratio of the two gas streams.
 6. A process according to claim 1 wherein the feed components light hydrocarbon, oxygen and ammonia are reacted in jet flames produced by a combustible gas mixture and the ammonia is admixed as the secondary gas stream into said flames.
 7. A process according to claim 1 wherein the feed components light hydrocarbon, oxygen and ammonia are reacted in jet flames produced by a combustible gas mixture and hydrogen or carbon monoxide is admixed as the secondary gas stream into said flames.
 8. A process according to claim 1 wherein the light hydrocarbon is selected from the group consisting of methane, ethane, propane and ethylene. 